The invention relates to “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, specifically implants to continuously monitor heart rhythm and deliver, if necessary, electrical pulses to the heart for stimulation, resynchronization and/or defibrillation in case of rhythm disorder detected by the device.
The invention relates, in general, to the in situ implantation of such devices provided at the distal end with an anchoring device adapted to penetrate the tissue of a body wall at the chosen implantation site.
A typical example of such an anchoring member is a projecting helical screw axially extending from the medical device body and adapted to penetrate the heart tissue by a screwing motion at the implantation site. However, this anchoring arrangement is not limitative of the invention, which also applies to other types of anchoring members, for example by implementation of needles, hooks, barbs, etc., penetrating tissue for permanently fixing the medical device.
According to a first aspect, the invention more particularly relates to those devices that are in the form of an autonomous capsule implanted in a heart chamber (ventricle, atrium or even arterial left heart chamber). The device will be hereinafter referred to as “autonomous capsule” or “leadless capsule” (the autonomous character of the capsule, albeit not intrinsically, being a necessary feature of the invention). These autonomous capsules are devoid of any physical connection to a main implanted device (such as the housing of a stimulation pulse generator) or not implanted device (external device such as a programmer or monitoring device for remote monitoring of the patient). Accordingly, the capsules are referred to as “leadless capsules”, to distinguish them from electrodes or sensors located at the distal end of a conventional lead, which is traversed throughout its length with one or more conductors galvanically connecting the electrode or sensor to a connected generator at an opposite, proximal, end to the lead.
It will be seen that, according to a second aspect, the invention can be generalized to the “delivery”. That is to say the implantation in the selected site of implantation of other types of medical devices. In one example, such devices may be stimulation leads in the form of a tubular body having at its distal end an anchoring mechanism for anchoring to a heart wall and an active portion provided with detection/stimulation electrodes, and at its proximal end, mechanical and electrical connection to the housing of a generator that is remotely implanted from the site of application of the pulses. The invention can be applied to still other types of implantable devices, for example to capsules intended for release in situ of an active pharmacological agent.
When the leadless capsules are endocardial capsules (capsules attached to the inner wall of an atrial or ventricular chamber, as opposed to epicardial capsules fixed to the external wall of the heart), the implantation constraints are increased because of the surgery approach. The approach for endocardial implantation involves going through the peripheral venous system and directs, under image intensifier, the capsule to the selected implantation site. This in a both precise and perfectly secure method. It is only once the site is reached and the capsule is firmly attached in the heart wall that the operator may proceed to the “release” of the capsule, or more particularly, its disconnection from the implantation accessory.
U.S. 2012/0095539 A1 discloses an implantation accessory for an endocardial electrostimulation leadless capsule. This accessory includes a steerable catheter carrying the capsule. The steerable catheter houses in its inner lumen at its end a wire which is distally connected to the capsule and which is operable in translation and rotation from the proximal end by a handle provided for the practitioner. In a first embodiment, the capsule is mounted to the catheter tip by a system of male/female nesting and the wire end is screwed to the back of the capsule. The retention wire keeps the two elements of the coupling system fitted into each other by a slight tension on the wire, the latter being locked in translation in the manipulation handle. In a second embodiment, the wire remains attached to the capsule after it has been separated from the catheter, so as to act as a safety wire in case it is necessary to reoperate on the capsule after implantation.
EP 2394695 A1 (Sorin CRM SAS) discloses another autonomous intracardiac capsule assembly with an implantation accessory. The capsule holds on the sidewall of the tubular body coupling fingers cooperating with a helical guide carried by the distal end of the implantation accessory. The direction of helix of the helical guide is opposite to that of the anchoring screw of the capsule, so as to transmit the screwing torque of the anchoring screw in the heart wall. Then after the front face of the capsule is coming to bear against this wall, the progressive separation of the capsule with the implantation accessory occurs by further screwing of the catheter causing the coupling fingers to slide between the turns of a helical compression spring. The torque limiter effect is thus being obtained by the compression of this helical spring.
The acceptance by practitioners of the technique of endocardial leadless capsules involves being able to offer a delivery system that is able to secure the implementation of these capsules and may include the following advantageous features:
Procedure similar to the current practice, which makes use of well-known and mastered practitioners gestures: subclavian or femoral puncture, insertion and manipulation of a catheter via preformed stylets during the approach phase of the selected implantation site, fastening of the screw or barb type, catheter manipulation of the electrophysiology type, etc.;
Standard environment of the operating room;
Limiting the risk of coring of the tissues due to excessive tightening which may damage the wall or worse, puncture it (especially in the case of implantation into a thin wall as the atrial septum or the apical region the right ventricle);
Possibility of intraoperatively or postoperatively removing and/or repositioning in case of problems, even after release of the capsule;
No risk of migration of the capsule during the acute phase response;
Certainty of a good fixation of the capsule before removing the implantation accessories, this constraint being the most critical of all;
System natively designed for a femoral approach (see below);
For vessels and heart chambers, no risk of damage by the anchoring member (screw, hook, needle, etc.) throughout the implantation method, including the navigation in the venous network and the approach phase to the selected implantation site;
Quick procedure, with an implantation target time of approximately 30 minutes ‘skin-to-skin’, comparable to that of the implantation of a generator and a conventional ventricular lead;
Safe operation, including in the case of: i) improper handling, with in this case inability to jettison the capsule if screwing of the anchoring member is incomplete, and/or ability to recover the capsule during the procedure, and ii) premature discontinuation of the procedure;
Low cost of manufacturing of the complete implantation system, notably through the use of proven technologies and components in similar applications.
A further difficulty arises with the current leadless capsules due to their relatively large dimensions, with a typical diameter of about 4-7 mm and a length of 15-40 mm. Indeed, to reach a heart chamber, and in particular to reach the apex of the right ventricle, with an object of this size there is no routine procedure by high approach, that is to say via the subclavian vein. It is therefore necessary to use a different approach, from a femoral puncture then to go back in the inferior vena cava to the heart.
Such a femoral approach is recognized as more difficult, especially because of the large angle between the inferior vena cava and the axis of the right ventricle. Indeed, in the case of a high approach, at the arrival in the atrium, the distal portion of the implantation catheter is naturally oriented towards the apex of the right ventricle. At this point, one just has to push the catheter through the tricuspid valve and reach the bottom of the ventricle, wherein the anchoring member may be screwed to the wall after landing. However, in the case of a femoral approach, once the atrium is reached it is necessary to perform a turning maneuver of the distal end of the catheter to guide the latter towards the ventricle and allow it to pass through the tricuspid valve and continue to progress in the right direction, towards the apex of the ventricle.
For this purpose, well-known steerable catheters exist, the tip of which is operated from the proximal handle so that it can perform such a reorientation maneuver in the atrium under image intensifier. But a final challenge remains in the final approach phase, as part of the steerable catheter may be too short or poorly shaped to allow docking with the wall of the ventricular apex.
There is therefore the need to have an implantation accessory for fine adjustment and precise approach of the implantation site with large differences in myocardium anatomy.